REM sleep behaviour disorder (RBD), which can anticipate by decades the onset of a neurodegenerative disease, in particular MSA and PD [66], has been reported in patients with CASPR2 and LGI1-antibody-associated limbic encephalitis [19,67,68] and with IgLON5-antibody linked neurodegeneration [45]. This evidence concerns the gene LGI1 and Parkinson disease.